ISLAMORADA -- An environmental restoration project now underway on Lower Matecumbe Key includes what one local botanist calls "the rarest plant habitat in Florida."

Early this month, the Florida Department of Transportation cleared invasive vegetation, including plenty of Brazilian pepper, from a 6.5-acre property along the Overseas Highway at mile marker 77.5.

The site was to be replanted late this summer with native vegetation. But the highway agency now plans to wait until spring in order to give the remnant Brazilian pepper mulch time to break down.

A variety of native plants and trees, including white mangroves, green buttonwood, seagrape, sea-oxeye daisy and blolly, are to be included in the planting.

The Lower Matecumbe property, which FDOT purchased in the 1970s for conservation, features a variety of habitats, including a coastal berm, wetlands and uplands.

But what has the local ecological community excited is its roughly half acre of Keys cactus barren.

Steve Hodges, a conservationist for the Key West Botanical Garden and Fairchild Tropical Botanic Garden in Miami, said only a half dozen such cactus barrens remain, and all but one are in the Middle and Upper Keys.

"This is probably the only chance that we'll ever get to actually restore one of these areas," he said.

Keys cactus barrens sit uniquely on land that is too high for mangroves and buttonwoods and too low for hardwood hammock. With their combination of exposed limestone and scruffy shrubs, they often don't look like much. But looks can be deceiving.

Keys cactus barrens house a wide variety of plants, many of which are threatened or endangered. Butterfly bush, limestone flatsedge, Poepig's rosemallow, Florida Keys indigo and skyblue clustervine are among the endangered species found just on FDOT's Lower Matecumbe site.

Other colorfully named plants that occur in the cactus barren ecosystem include Yucatan fly mallow, hurricane grass, wild bushbean and dwarf morning glory, to name just a few.

There are actually four patches of cactus barren, covering a total of 0.6 acres, on the Lower Matecumbe FDOT property. Those areas were never overgrown by Brazilian pepper, though that could have happened eventually if the site had not been cleared.

FDOT has wanted to restore the property ever since Hodges discovered the cactus barrens approximately seven years ago, said John Palenchar, the agency's environmental permits specialist. However, the agency hadn't been able to commit to the $280,000 expenditure.

The opportunity arose as a result of a planned widening of the Overseas Highway on Grassy Key next year. That project will include the removal of wetlands along the right-of-way, which means FDOT has to mitigate the damage elsewhere.

"That kind of gave us the green light to justify the investment," Palenchar said.

As part of the restoration, the Key West Botanical Gardens plans to introduce endangered cactus barren species that aren't already on the site.

"We definitely knew we had something very special at this location," Palenchar said.